Strengthening FCC-CoCrFeMnNi high entropy alloys by Mo addition

In order to strengthen the face-centered-cubic (FCC) type CoCrFeMnNi high entropy alloys (HEAs), different contents of Mo (0–16 at.%, similarly hereinafter) were alloyed. Phase evolution, microstructure, mechanical properties and related mechanism of these HEAs were systematically studied. The results show that sigma phase is appeared with addition of Mo, and the volume fraction of it increases gradually from 0 to 66% with increasing Mo content. It is found that Mo is enriched in sigma phase, which indicates that Mo element is beneficial to form sigma phase. Compressive testing shows that the yield strength of the alloys increases gradually from 216 to 765 MPa, while the fracture strain decreases from 50% (no fracture) to 19% with increasing of Mo. The alloy exhibits the best compressive performance when Mo content reaches 11%, the yield strength, fracture strength and fracture strain are 547 MPa, 2672 MPa and 44% respectively. The increased volume fraction of sigma phase plays an important role in improving the compressive strength of (CoCrFeMnNi)_{100- x}Mo_x HEAs.